Set in a single location, the film (in select Canadian theatres April 21) finds the British director hitting his sweet spot, delivering a thought-provoking picture about gun violence, power and masculinity, while still keeping it an entirely entertaining action thriller.

Critics have drawn comparisons to the early work of Quentin Tarantino and Martin Scorsese (the latter of whom is also executive producer), but speaking with Exclaim! at the Toronto International Film Festival this past September, Wheatley was quick to downplay its early accolades.

"I made it for me," he says, "but I was gambling that it would be something everyone else wanted to see."

Here, the Brighton-based filmmaker shares a few facts about the making of his latest movie.

"I think it's really important that everything's relaxed, making an atmosphere where there's no failure, no judgement. The world of the shout-y director and the egotistical director is bizarre to me," he says. "Actors, camera department — you've got to get them on side and they'll give you everything, if it's right."

2 He wanted to make a movie where each character was equally vulnerable.

"The idea that a gun will kill you like a laser beam, or a pistol anyway, is a thing that's kind of a Hollywood construct. I wanted to see what happened when everyone hit the ground," Wheatley says. "It's like when you walk into the woods on a summer day and you think 'Ahh, cool, it's all going to be cool.' And then you lose your way and you realize that the woods can actually kill you quite quick if you're fucking stupid."

3 Every moment was mapped out in detail ahead of time.

Once things get going, it's pretty clear that Free Fire is more than meets the eye. To make sure everything — from injuries to weapons being fired (and at what or whom) — made sense, Wheatley and his crew started mapping out the action by using toy soldiers and a model car kit. Once they found a suitable warehouse space for the film, they graduated to Nerf guns and cardboard boxes taped together as pillars to figure out the sightlines and further orchestrate the action.

"So it was really meticulous," he says. "It had to be."

4 Unlike most films, Free Fire was shot chronologically because it would have been too confusing to do it otherwise.

"It would have been really hard to keep track of the wounds and stuff and destruction in the building," Wheatley says. "The script itself is structured in terms of goals and tiny missions, one after the other after the other. It gets to the point where there's a crescendo and then it kind of releases back down again, because you couldn't just go full tilt the whole time."

5 One of the harder casting decisions was getting the right actor to lie on the ground for almost a month during filming.

At one point in the film, a certain character suffers a head injury and is presumed dead. Although they lie motionless on screen for well over 30 minutes, Wheatley says casting the role became a peculiar problem.

"It was a big production worry… Because there's a bit of acting at the beginning, but then they have to lie in a fucking hole for three weeks," he says. "We had a few conversations."